There are a number of reasons why it is important to minimize the weight of a brake disk (also sometimes referred to as a brake rotor). First, the weight of the brake disk contributes to the overall weight of the vehicle, and in this respect, affects the vehicle's fuel efficiency and performance. Additionally, the weight of the brake disk adds to the vehicles “unsprung weight” which is generally considered to be the primary source of vehicle noise and vibration. In addition, less energy is required to rotate a relatively light brake disk during vehicle travel, and accordingly, a reduction in brake disk weight is generally accompanied by an increase in the vehicle's fuel efficiency and performance. A final consideration, which is especially important for brake disks used on motorcycles, for example, is the effect of brake disk weight on the motorcycle's handling characteristics. In greater detail, gyroscopic inertia is generated when a brake disk is rotated. Specifically, for a given rotation velocity, a heavy brake disk generates more gyroscopic inertia that a light brake disk. This gyroscopic inertia, in turn, must be overcome by the rider to steer the motorcycle. The result is that a heavier brake disk adversely affects a motorcycle's handling characteristics.
During braking, hydraulic (or mechanical) energy is used to press the vehicle's brake pads against the rotating brake disk. The friction resulting from the moving contact between brake pad and brake disk slows the rotation of the brake disc and decreases the speed of the vehicle. This frictional contact generates heat and causes the contact surfaces on the brake pad and brake disk to wear unevenly. Excessive wear can cause the brake disk to become thin and weak. In some cases, the thinning of the brake disk becomes so severe that the brake disk is no longer able to support the stresses and heat generated during braking. The result is typically a warped brake disk that can cause undesirable brake chattering.
Conventional brake disks have typically been made of cast iron. Cast iron is relatively inexpensive, machines freely and has adequate strength and wear resistance at the relatively high brake system service temperatures. On the other hand, cast iron brake disks are relatively heavy due to the high density of cast iron. For example, the density, .rho., of cast iron is approximately 7.4 gms/cc compared to light metals such as aluminum (.rho.congruent.2.7 gms/cc) and Titanium (.rho.congruent.4.5 gms/cc).
A final factor that must be considered when designing brake rotors is aesthetics. Modern racing motorcycles have rather large diameter brake disks that are plainly visible, especially the front disk. Because of this visibility, the color and surface appearance of a brake disk can add to or detract from the overall look of the motorcycle. These considerations can affect a purchaser's decision when buying a new motorcycle and when retrofitting a motorcycle with a new brake system.
In light of the above, it is an object of the present invention to provide lightweight brake disks with better functionality.